The avermectin compounds have been disclosed in a series of patents starting with U.S. Pat. No. 4,310,519 to Albers-Schoenberg, et al. The milbemycin compounds have been disclosed in a series of patents starting with U.S. Pat. No. 3,950,360 to Aoki, et al. All of the avermectins and milbemycins are characterized in having a 16-membered macrocyclic ring fused to a spiroketal ring system composed of two 6-membered rings. No references are known where this ring systems has been changed from the natural 6,6-system to the instant 6,5-system.